Tube-type heat exchangers include a plurality of tubes of substantially uniform length and a plurality of truncated, perforated baffles through which the tubes pass. Such assembled tube and baffle arrangements are referred to herein as a “bundle assembly.” Tube and baffle bundle assemblies can be assembled manually and/or automatically. Whether assembled manually, automatically, or by combination of manual and automatic methods, the resulting bundle assembly must conform to a predetermined desired shape, size, and configuration. This is because, after full assembly, the bundle assembly is typically inserted into a heat exchanger shell having predetermined fixed internal dimensions and overall length, such as in the shell of an oil cooler in a vehicle. Any significant deviation in the dimensions of the finished bundle assembly can prevent proper fit and proper function of the assembly within the heat exchanger shell.
Automatic tube assembly machines of the type with which this invention is used are illustrated in commonly owned U.S. Pat. Nos. 3,789,479 and 4,785,518. Such machines include, for example, a tube and baffle holding fixture mounted on a work table having capacity for selected vertical and horizontal movements. Two opposing sets of retractable guide rods advance successively selected quantities of tubes from a supply to the fixture, the individual rods of each set being aligned with corresponding rods of the opposing set. The machine includes means automatically operative to actuate the guide rods to advance the selected quantities of tubes from the supply to the fixture, means automatically operative to adjust the work table vertically and horizontally, following each transfer of tubes, to prepare for the transfer of the next selected quantity of tubes, and control means governing the movements of the guide rods and the work table. In this manner, tubes can be accurately and efficiently inserted to penetrate through one or more baffles in series, thereby forming a bundle assembly having a preselected configuration and dimension.
In some bundle assemblies, the perforated baffles are constituted of relatively thin, rigid metal sheets well adapted to withstand, without distortion of movement, the axial forces occurring as a result of the penetrations of the guide rods and the tubes back and forth through the baffle apertures during assembly of the bundle assembly. However, in some installations, it is preferred that the baffles be constituted of a non-metallic material, such as a relatively soft, pliable or flexible gasket-like composite material, referred to herein as “composite baffles”, which is readily bendable or otherwise distortable when subjected to relatively minor degrees of force. In forming the perforations in such composite baffles, the dies utilized for stamping the perforations in metal baffles also are used for forming the perforations in the composite baffles. Following stamping, the perforations or holes in the composite baffles have a tendency to change diameter-wise. Such phenomenon, while not at all undesirable as far as the completed heat exchanger bundle assembly is concerned, renders difficult the assembly of its tubes and baffles.
Additionally, in some installations, it is preferred that the baffles be constituted of a tough, rigid, high-strength amorphous thermoplastic. Following molding of the baffle, the holes in the baffle have a tendency to change in a diameterwise manner. In the case of amorphous thermoplastic baffles, the variation is generally predictable, and therefore, the baffle design includes holes that are oversized to accommodate the material movement without producing a surface to surface or interference fit with the tubes in the assembly process. Such phenomenon renders difficult the movement of in-process bundle assemblies in the manufacturing process and cured heat exchanger assemblies in transit between the heat exchanger assembly process, and also in the processes used to join the heat exchanger bundle assemblies with the shell.
Because of the flexible character of composite baffles, and because of the tendency of their perforations to dimensionally change, heat exchanger bundle assemblies incorporating such baffles are extremely difficult to assemble by machine and nearly impossible to assemble by hand. Because of the loose hole condition of the plastic baffles, and their effect on the dimensional and quality characteristics of the tube assembly product, bundle assemblies using plastic baffles are also difficult to fixture during the production process to match a predetermined configuration.
Additionally, once assembled, tube-type heat exchanger bundle assemblies, whether having metallic, plastic, and/or composite baffles, can easily become undesirably twisted or otherwise deformed from the desired predetermined configuration and dimensions, rendering them unsuitable for insertion into corresponding shell or housings to function as a heat exchanges such as an oil cooler, for example. Therefore, what is needed are assembly and fixturing apparatus and methods that will create and permanently preserve the desired configuration, shape and dimensions of a tube and baffle heat exchanger bundle assembly.
Lastly, it has been observed that vibration commonly encountered within a tube and baffle assembly within a heat exchanger casing may result in wear, and even cutting, of the tubes by the baffles. Thus, there is a further need for tube and baffle bundle assemblies that can withstand, and also attenuate, undesired vibrational contact between the tubes, baffles, and casing.